Known low-irritative solid detergent compositions comprise anionic surfactants having near neutral pH values (for example, sodium lauryl sulfate) or weakly acidic surfactants (for example, sodium N-acylglutamate), either alone or together with a soap. There have also been known detergents wherein fatty acid triethanolamine salts are used as a soap base in order to reduce the effects of free alkalis contained in soaps as disclosed, for example, in Fragrance Journal, vol. 47, page 47 (1981) Recently, it has been furthermore reported that a low-irritative solid detergent composition can be obtained by adding an alkyl sulfosuccinate or an ethylene oxide adduct salt thereof to a soap base as disclosed, for example, in JP-A-2-155991 (the term "JP-A" as used herein means an "unexamined published Japanese Patent Application").
However, these low-irritative solid detergents are still unsatisfactory from the viewpoint of irritation, because they have an excessively high detergency or a pH value of 8 to 9. In addition, they have an undesirable feel during washing. Namely, they have a sticky or slimy feel during use or give a stretched or dry/rough feel after drying. When synthetic surfactants are used as a detergent base, on the other hand, the shape of the solid detergent compositions is easily deformed and have poor strength upon molding, compared with common soaps.
Accordingly, an objective of the present invention is to provide a less irritative solid detergent composition which gives a good feel during and after use and has an excellent solidity.
Under these circumstances, the present inventors have conducted extensive investigations. Consequently, the inventors found that a solid detergent composition, which has an appropriate detergency and good foaming properties characteristic of detergent compositions, is less irritative than conventional detergent compositions and gives a good feel during and after use, can be obtained by adding a specific N-acyl compound of a secondary amide type, as a detergent base, to higher fatty acid(s) or higher alcohol(s).